不同离子对防城港近海养殖区溶解性有机质光化学行为的影响研究OA

Under light irradiation,dissolved organic matter(DOM)undergoes photochemical reactions and produc-es reactive oxygen species(ROS)such as triplet-state DOM(3DOM*),singlet oxygen(1O2),and hydroxyl radical(•OH),thereby playing a crucial role in the degradation of marine organic contaminants.However,ROS generation from DOM in the offshore aquaculture areas of the Beibu Gulf,as well as the role of coexisting ions in these pro-cesses,remains largely unexplored.In this study,the composition of DOM,the generation of ROS,and the influ-encing factors in the offshore aquaculture area of Fangchenggang,Beibu Gulf,were investigated using an integrated approach combining three-dimensional excitation-emission matrix(EEM)fluorescence spectroscopy with photo-chemical experiments.Results revealed that DOM comprised humic-like and protein-like fractions.Combined analyses of fluorescence,biological,and humification indices indicated that the DOM in this region was predomi-nantly endogenous,with a mixed endogenous-exogenous character and a low degree of humification.During this process,the formation rates of 3DOM*,1O2,and •OH were on the order of 10-9,10-8,and 10-12 mol·L-1·s-1,with the corresponding steady-state concentrations of 10-15,10-14,and 10-18 mol/L,respectively.Both the formation rates and steady-state concentrations observed were generally lower than those reported for typical freshwater environ-ments.The steady-state concentration of 3DOM* decreased with increasing Cl-concentration,whereas its formation rate slightly increased with higher Br-concentration,confirming that bromine,as a heavy atom,promotes intersys-tem crossing and the conversion of 1DOM* to 3DOM*.In addition,higher concentrations of Br-acted as a scavenger,thereby lowering the steady-state concentration of •OH.At seawater-relevant concentrations,metal ions such as Cu2+and Fe3+had a negligible effect on the steady-state concentrations of 3DOM* and 1O2,but enhanced •OH pro-duction through Fenton-like reactions.Overall,this study investigates the photochemical generation of ROS from DOM extracted from the offshore aquaculture area of the Beibu Gulf and compares the response of these processes to typical coexisting halide and metal ions.These findings provide a deeper mechanistic understanding of DOM-mediated photochemical processes involving organic contaminants in seawater and ultimately help assess environmental risks and develop management strategies to reduce their impact.